A study published in the journal Cancer suggests that post-diagnosis consumption of foods containing isoflavones—estrogen-like compounds primarily found in soy food—may be associated with a decrease in all-cause mortality for women with some breast cancers.
The researchers analyzed data on 6,235 American and Canadian breast cancer patients from the Breast Cancer Family Registry, a National Cancer Institute-funded program that has collected clinical and questionnaire data on enrolled participants and their families since 1995. Women were sorted into four quartile groups based on the amount of isoflavone they were estimated to have consumed, calculated from self-reported food frequency questionnaires. Mortality was examined after a median follow-up of 9.4 years.
The researchers found a 21% decrease in all-cause mortality among women in the highest quartile of intake, when compared to those in the lowest quartile. The association between isoflavone intake and reduced mortality was strongest in women with tumors that lacked estrogen and progesterone receptors. Women who did not receive endocrine therapy as a treatment for their breast cancer had a weaker, but still significant association. No associations were found for women with hormone-receptor-positive tumors and for women who received endocrine therapy.
The large size and diverse racial/ethnic makeup of the Breast Cancer Family Registry allowed the researchers to evaluate mortality risk across different subtypes of breast cancer and subgroups of patients, and adjust for confounding factors. However, the authors note that dietary isoflavone intake was correlated with socioeconomic and lifestyle factors, which may also play a role in lowering mortality. In particular, women who consumed higher levels of dietary isoflavone were more likely to be Asian Americans, young, physically active, more educated, not overweight, never smokers, and drink no alcohol. Although the team controlled for these factors in the analyses, the possibility of a partial confounding effect on the associations identified in the study cannot be ruled out.